Inflammatory and hypoxic stress-induced islet exosomes released during isolation are associated with poor transplant outcomes in islet autotransplantation.

Islets experience enormous stress during the isolation process, leading to suboptimal endocrine function after total pancreatectomy with islet autotransplantation (TPIAT). Our investigation focused on inducing isolation stress in islets ex vivo, where proinflammatory cytokines and hypoxia prompted the release of stress exosomes (exoS) sized between 50 and 200 nm. Mass spectrometry analysis revealed 3 distinct subgroups of immunogenic proteins within these exoS: damage-associated molecular patterns (DAMPs), chaperones, and autoantigens. The involvement of endosomal-sorting complex required for transport proteins including ras-associated binding proteins7A, ras-associated binding protein GGTA, vacuolar protein sorting associated protein 45, vacuolar protein sorting associated protein 26B, and the tetraspanins CD9 and CD63, in exoS biogenesis was confirmed through immunoblotting. Next, we isolated similar exoS from the islet infusion bags of TPIAT recipients (N = 20). The exosomes from infusion bags exhibited higher DAMP (heat shock protein family A [Hsp70] member 1B and histone H2B) levels, particularly in the insulin-dependent TPIAT group. Additionally, elevated DAMP protein levels in islet infusion bag exosomes correlated with increased insulin requirements (P = .010) and higher hemoglobin A1c levels 1-year posttransplant. A deeper exploration into exoS functionality revealed their potential to activate monocytes via the toll-like receptor 3/7: DAMP axis. This stimulation resulted in the induction of inflammatory phenotypes marked by increased levels of CD68, CD80, inducible nitric oxide synthase, and cyclooxygenase-2. This activation mechanism may impact the successful engraftment of transplanted islets.

Single incision simultaneous liver kidney transplantation: Feasibility and outcomes.

BACKGROUND: Traditionally, simultaneous liver kidney transplantation (SLK) has been performed using a subcostal incision for the liver allograft and a lower abdominal incision for kidney transplantation (dual incision, DI). At our institution, we performed SLK using a single subcostal incision (SI). The aim of this study was to report the outcomes of single versus dual incisions for SLK. METHODS: A retrospective cohort study of consecutive SLK procedures performed at our center from January 2015 to April 2021 was performed. The demographic characteristics, complications, intraoperative findings, and complications after SI and DI were statistically compared. RESULTS: A total 37 SLK were performed (19 DI and 18 SI). The age and indications for transplantation were comparable between the two groups. Patient in SI group had significantly higher MELD score (27.0 ± 1.5 vs. 31.7 ± 1.5, p = .038). The cold ischemic time of kidney transplantation (599 ± 26 min vs. 447 ± 27 min, p < .001) and the total surgical time (508 ± 21 min vs. 423 ± 22 min, p = .008) were significantly shorter in the SI group. The incidence of complications and post-transplant kidney function was comparable between the groups. A slightly higher incidence of surgical site complications was noted in the DI group without any statistically significance (p = .178). CONCLUSIONS: Single-subcostal incision SLK is technically feasible and has comparable outcomes to dual-incision SLK. SI was associated with shorter cold ischemic time for kidney transplant, as well as shorter overall operative time.

Liver transplantation for post-COVID-19 cholangiopathy: A case series.

BACKGROUND: Post-COVID-19 cholangiopathy is an emerging cholestatic liver disease observed in patients recovering from severe COVID-19 infection. Its prognosis is poor, necessitating liver transplantation in some cases. This study aimed to investigate the outcomes of liver transplantation for post-COVID-19 cholangiopathy. METHODS: Seven patients who underwent liver transplantation for post-COVID-19 cholangiopathy at three institutions between 2020 and 2022 were included in this retrospective multi-center case series. RESULTS: At the time of initial COVID-19 infection, all patients developed acute respiratory distress syndrome, and six patients (86%) required ICU admission. Median time intervals from the initial COVID-19 diagnosis to the diagnosis of post-COVID-19 cholangiopathy and liver transplantation were 4 and 12 months, respectively. Four patients underwent living donor liver transplantation, and three patients underwent deceased donor liver transplantation. The median MELD score was 22 (range, 10-38). No significant intraoperative complications were observed. The median ICU and hospital stays were 2.5 and 12.5 days, respectively. One patient died due to respiratory failure 5 months after liver transplantation. Currently, the patient and graft survival rate is 86% at a median follow-up of 11 months. CONCLUSIONS: Liver transplantation is a viable option for patients with post-COVID-19 cholangiopathy with acceptable outcome. Timely identification of this disease and appropriate management, including evaluation for liver transplantation, are essential.

The demise of islet allotransplantation in the United States: A call for an urgent regulatory update.

Islet allotransplantation in the United States (US) is facing an imminent demise. Despite nearly three decades of progress in the field, an archaic regulatory framework has stymied US clinical practice. Current regulations do not reflect the state-of-the-art in clinical or technical practices. In the US, islets are considered biologic drugs and "more than minimally manipulated" human cell and tissue products (HCT/Ps). In contrast, across the world, human islets are appropriately defined as "minimally manipulated tissue" and not regulated as a drug, which has led to islet allotransplantation (allo-ITx) becoming a standard-of-care procedure for selected patients with type 1 diabetes mellitus. This regulatory distinction impedes patient access to islets for transplantation in the US. As a result only 11 patients underwent allo-ITx in the US between 2016 and 2019, and all as investigational procedures in the settings of a clinical trials. Herein, we describe the current regulations pertaining to islet transplantation in the United States. We explore the progress which has been made in the field and demonstrate why the regulatory framework must be updated to both better reflect our current clinical practice and to deal with upcoming challenges. We propose specific updates to current regulations which are required for the renaissance of ethical, safe, effective, and affordable allo-ITx in the United States.

The role of total pancreatectomy with islet autotransplantation in the treatment of chronic pancreatitis: A report from the International Consensus Guidelines in chronic pancreatitis.

BACKGROUND: Advances in our understanding of total pancreatectomy with islet autotransplantation (TPIAT) have been made. We aimed to define indications and outcomes of TPIAT. METHODS: Expert physician-scientists from North America, Asia, and Europe reviewed the literature to address six questions selected by the writing group as high priority topics. A consensus was reached by voting on statements generated from the review. RESULTS: Consensus statements were voted upon with strong agreement reached that (Q1) TPIAT may improve quality of life, reduce pain and opioid use, and potentially reduce medical utilization; that (Q3) TPIAT offers glycemic benefit over TP alone; that (Q4) the main indication for TPIAT is disabling pain, in the absence of certain medical and psychological contraindications; and that (Q6) islet mass transplanted and other disease features may impact diabetes mellitus outcomes. Conditional agreement was reached that (Q2) the role of TPIAT for all forms of CP is not yet identified and that head-to-head comparative studies are lacking, and that (Q5) early surgery is likely to improve outcomes as compared to late surgery. CONCLUSIONS: Agreement on TPIAT indications and outcomes has been reached through this working group. Further studies are needed to answer the long-term outcomes and maximize efforts to optimize patient selection.

Risk factors for early readmission after total pancreatectomy and islet auto transplantation.

BACKGROUND: Little published data exist examining causes of hospital readmission following total pancreatectomy with islet autotransplantation (TPIAT). METHODS: A retrospective analysis was performed of a prospectively collected institutional TPIAT database. Primary outcome was unplanned readmission to the hospital within 30 days from discharge. Reasons and risk factors for readmission as well as islet function were evaluated and compared by univariate and multivariate analysis. RESULTS: 83 patients underwent TPIAT from 2006 to 2014. 21 patients (25.3%) were readmitted within 30 days. Gastrointestinal problems (52.4%) and surgical site infection (42.8%) were the most common reasons for readmission. Initial LOS and reoperation were risk factors for early readmission. Patients with delayed gastric emptying (DGE) were three times more likely to get readmitted. In multivariate analysis, patients undergoing pylorus preservation surgery were nine times more likely to be readmitted than the antrectomy group. CONCLUSION: Early readmission after TPIAT is common (one in four patients), underscoring the complexity of this procedure. Early readmission is not detrimental to islet graft function. Patients undergoing pylorus preservation are more likely to get readmitted, perhaps due to increased incidence of delayed gastric emptying. Decision for antrectomy vs. pylorus preservation needs to be individualized.

A study of the clinical utility of a 20-minute secretin-stimulated endoscopic pancreas function test and performance according to clinical variables.

BACKGROUND AND AIMS: Direct pancreas juice testing of bicarbonate, lipase, or trypsin after stimulation by secretin or cholecystokinin is used to determine exocrine function, a surrogate for diagnosing chronic pancreatitis (CP). Endoscopic pancreas function tests (ePFTs), where a peak bicarbonate concentration (PBC) ≥80 mEq/L in pancreas juice is considered normal, are now used more frequently. In this ePFT, aspirates start 35 minutes after secretin administration because pancreas output peaks 30 minutes after secretagogue administration. The performance of ePFT in a cohort of patients with a presumptive diagnosis of CP referred to a pancreas clinic for consideration of an intervention including total pancreatectomy and islet autotransplantation was studied, compared with EUS, ERCP, histology, and consensus diagnosis. The effect of sedation, narcotic use, aspirate volume, body mass index, age, and proton pump inhibitors (PPIs) on test performance is reported. METHODS: After a test dose, synthetic human secretin was administered intravenously, and 30 minutes later sedation was achieved with midazolam and fentanyl or propofol. A gastroscope was advanced to the major papilla where 4 continuous aspiration samples were performed at 5-minute intervals in sealed bottles. PBC ≥80 mEq/L was normal. RESULTS: Eighty-one patients had ePFTs from August 2010 through October 2015. Twenty-seven patients (33%) were diagnosed with CP. Eighteen of the 27 patients with CP and 1 of the 54 patients without CP had an abnormal ePFT, producing a sensitivity of 66% (95% CI, 46.0-83.5), specificity 98% (95% CI, 90.1-99.9), positive predictive value 94.7% (95% CI, 74-99.9), and negative predictive value 85.5% (95% CI, 74.2-93.1). ERCP and PBC concordance was generally poor, but none of the patients without CP had major EUS changes, and only 3 patients with a PBC <80 mEq/L had a normal EUS. The PBC was affected by narcotics and PPI use. CONCLUSION: A 20-minute ePFT after secretin administration had a marginal sensitivity for diagnosis of CP. The diagnosis of CP should not rely on a single study and certainly not a PFT. The duodenal aspirate volume did not correlate with the PBC, which contrasts with current secretin-enhanced MRCP knowledge; therefore, further studies on this subject are warranted. Neither type of sedation, BMI, nor age affected test performance. Narcotics and PPIs may affect the PBC, so borderline results should be interpreted with caution in these groups.

Essential phospholipids prevent islet damage induced by proinflammatory cytokines and hypoxic conditions.

BACKGROUND: The pancreatic islet damage that occurs through an inflammatory response and hypoxia after infusion is a major hurdle in islet transplantation. Because essential phospholipids (EPL) have been shown to exhibit anti-inflammatory properties in liver disease, we analysed their protective effect on islets in inflammatory or hypoxic conditions. METHODS: We evaluated the viability of mouse and human islets cultured with cytokines or in hypoxic conditions for 48 h and measured cytokine expression in islets by quantitative polymerase chain reaction. We then employed an in vivo mouse assay, transplanting a marginal dose of human islets treated with or without EPL into the subcapsule of the kidney in diabetic nude mice and determining the cure rate. RESULTS: The viability of mouse and human islets damaged by cytokines was significantly improved by supplementation of EPL in the culture (p = 0.003 and <0.001 for mouse and human islets respectively). EPL significantly inhibited intracellular expression of IL-1ß and IL-6 in cytokine-damaged human islets (p < 0.001). The viability of human islets in hypoxic conditions was significantly better when treated with EPL (p < 0.001). In the in vivo mouse assay, the EPL-treated islet group had a higher cure rate than the untreated control, with marginal statistical significance (75 and 17% respectively, p = 0.07). CONCLUSIONS: EPL could be a potent agent to protect islets from inflammatory and hypoxic conditions after isolation procedures. Further studies to clarify the effect of EPL in islet transplantation are warranted.

Improving allogeneic islet transplantation by suppressing Th17 and enhancing Treg with histone deacetylase inhibitors.

Islet transplantation is a new treatment for achieving insulin independence for patients with severe diabetes. However, major drawbacks of this treatment are the long graft survival, the necessity for immunosuppressive drugs, and the efficacy of transplantation. Donor-specific transfusion (DST) has been shown to reduce rejection after organ transplantation, potentially through enhanced regulatory T-cell (Treg) activity. However, recent findings have shown that activated Treg can be converted into Th17 cells. We focused on histone deacetylase inhibitors (HDACi) because it was reported that inhibition of HDAC activity prevented Treg differentiation into IL17-producing cells. We therefore sought to enhance Treg while suppressing Th17 cells using DST with HDACi to prolong graft survival. To stimulate Treg by DST, we used donor splenocytes. In DST with HDACi group, Foxp3 mRNA expression and Treg population increased in the thymus and spleen, whereas Th17 population decreased. qPCR analysis of lymphocyte mRNA indicated that Foxp3, IL-10, and TGF-b expression increased. However, interleukin 17a, Stat3 (Th17), and IFN-g expression decreased in DST + HDACi group, relative to DST alone. Moreover, DST treated with HDACi prolonged graft survival relative to controls in mice islet transplantation. DST with HDACi may therefore have utility in islet transplantation.

Ratio of hepatic arterial flow to recipient body weight predicts biliary complications after deceased donor liver transplantation.

OBJECTIVES: Adequate hepatic arterial (HA) flow to the bile duct is essential in liver transplantation. This study was conducted to determine if the ratio of directly measured HA flow to weight is related to the occurrence of biliary complications after deceased donor liver transplantation. METHODS: A retrospective review of 2684 liver transplants carried out over a 25-year period was performed using data sourced from a prospectively maintained database. Rates of biliary complications (biliary leaks, anastomotic and non-anastomotic strictures) were compared between two groups of patients with HA flow by body weight of, respectively, <5 ml/min/kg (n = 884) and ≥5 ml/min/kg (n = 1800). RESULTS: Patients with a lower ratio of HA flow to weight had higher body weight (92 kg versus 76 kg; P < 0.001) and lower HA flow (350 ml/min versus 550 ml/min; P < 0.001). A lower ratio of HA flow to weight was associated with higher rates of biliary complications at 2 months, 6 months and 12 months (19.8%, 28.2% and 31.9% versus 14.8%, 22.4% and 25.8%, respectively; P < 0.001). CONCLUSIONS: A ratio of HA flow to weight of < 5 ml/min/kg is associated with higher rates of biliary complications. This ratio may be a useful parameter for application in the prevention and early detection of biliary complications.

Initial Experience With Robotic Liver Resection in the United States.

BACKGROUND: This study's aim was to show the feasibility and safety of robotic liver resection (RLR) even without extensive experience in major laparoscopic liver resection (LLR). METHODS: A single center, retrospective analysis was performed for consecutive liver resections for solid liver tumors from 2014 to 2022. RESULTS: The analysis included 226 liver resections, comprising 127 (56.2%) open surgeries, 28 (12.4%) LLR, and 71 (31.4%) RLR. The rate of RLR increased and that of LLR decreased over time. In a comparison between propensity score matching-selected open liver resection and RLR (41:41), RLR had significantly less blood loss (384 ± 413 vs 649 ± 646 mL, P = .030) and shorter hospital stay (4.4 ± 3.0 vs 6.4 ± 3.7 days, P = .010), as well as comparable operative time (289 ± 123 vs 290 ± 132 mins, P = .954). A comparison between LLR and RLR showed comparable perioperative outcomes, even with more surgeries with higher difficulty score included in RLR (5.2 ± 2.7 vs 4.3 ± 2.5, P = .147). The analysis of the learning curve in RLR demonstrated that blood loss, conversion rate, and complication rate consistently improved over time, with the case number required to achieve the learning curve appearing to be 60 cases. CONCLUSIONS: The findings suggest that RLR is a feasible, safe, and acceptable platform for liver resection, and that the safe implementation and dissemination of RLR can be achieved without solid experience of LLR.

'Burn and Push' technique: A novel robotic liver parenchymal transection technique.

BACKGROUND: Liver parenchymal transection during robotic liver resection (RLR) remains a significant challenge due to the limited range of specialised instruments. This study introduces our 'Burn and Push' technique as a novel approach to address these challenges. METHODS: A retrospective analysis was conducted on 20 patients who underwent RLR using the 'Burn and Push' technique at Virginia Commonwealth University Health System from November 2021 to August 2023. The study evaluated peri- and post-operative outcomes. RESULTS: The median operation time was 241.5 min (range, 90-620 min), and the median blood loss was 100 mL (range, 10-600 mL). Major complications occurred in one case, with no instances of postoperative bleeding, bile leak, or liver failure. CONCLUSIONS: The 'Burn and Push' technique is a viable and efficient alternative for liver parenchymal transection in RLR. Further research with larger sample sizes and consideration of the learning curve is necessary to validate these findings.

CD11b(+) cells in donor-specific transfusion prolonged allogenic skin graft survival through indoleamine 2,3-dioxygenase.

The aim of this study is to show the effect of donor-specific transfusion (DST) in inducing immunological tolerance mediated by regulatory T cells (Treg) and indoleamine 2,3-dioxygenase (IDO). Skin grafts from H2(d) Balb/c were transplanted into H2(k) C3H/He 7days after the infusion of donor splenocytes, isolated each immune cell populations. Graft survival prolonged in recipients who received splenocytes, MHC class II(+) CD90(-) cells and CD3(-)CD19(-) cells (p<0.001, p<0.05 and p<0.01, respectively). CD11b(+) cell infusion resulted in prolongation of graft survival when compared to CD11c(+) cell infusion (p<0.01). Foxp3(+)CD4(+)CD25(+) T cells were increased after the transplant in recipients infused with CD11b(+) cells (p<0.05). The mixed lymphocyte reaction showed donor-specificity (p<0.001). High IDO expression was observed in CD11b(+) cell infusion group. Graft survival with DST using IDO antagonist (1MT) were not prolonged. In conclusion, DST allows induction of donor-specific tolerance which involves Foxp3(+)CD4(+)CD25(+) T cells and IDO expression.

Tumor biology and pre-transplant locoregional treatments determine outcomes in patients with T3 hepatocellular carcinoma undergoing liver transplantation.

Liver transplantation is the optimal treatment for patients with hepatocellular carcinoma (HCC) and cirrhosis. This study was conducted to determine the impact of pre-transplant locoregional therapy (LRT) on HCC and our institution's experience with expansion to United Network of Organ Sharing Region 4 T3 (R4T3) criteria. Two hundred and twenty-five patients with HCC (176 meeting Milan and 49 meeting R4T3 criteria) underwent liver transplantation from 2002 to 2008. Compared with the Milan criteria, HCCs in R4T3 criteria displayed less favorable biological features such as higher median alpha-fetoprotein level (21.9 vs. 8.5 ng/mL, p = 0.01), larger tumor size, larger tumor number, and higher incidence of microvascular invasion (22% vs. 5%, p = 0.002). As a result, patients meeting Milan criteria had better five-yr survival (79% vs. 69%, p = 0.03) and a trend toward lower HCC recurrence rates (5% vs. 13%, p = 0.05). Pre-transplant LRT did not affect post-transplant outcomes in patients meeting Milan criteria but did result in lower three-yr HCC recurrence (7% vs. 75%, p < 0.001) and better three-yr survival (p = 0.02) in patients meeting R4T3 criteria. Tumor biology and pre-transplant LRT are important factors that determine the post-transplant outcomes in patients with HCC who meet R4T3 criteria.

Exosomes in transplantation: Role in allograft rejection, diagnostic biomarker, and therapeutic potential.

Exosomes are 50-200 nm-sized extracellular vesicles that are secreted by cells to transfer signals and communicate with other cells. Recent research has revealed that allograft-specific exosomes containing proteins, lipids, and genetic materials are released into circulation post-transplantation which are powerful indicators of graft failure in solid-organ and tissue transplantations. The macromolecular content of exosomes released by the allograft and the immune cells serve as potential biomarkers for assessing the function and the acceptance/rejection status of the transplanted grafts. Identifying these biomarkers could aid in the development of therapeutic strategies to improve graft longevity. Exosomes can be used to deliver therapeutic agonists/antagonists to grafts and prevent rejection. Inducing long-term graft tolerance has been demonstrated in many studies using exosomes from immunomodulatory cells such as immature DCs, T regulatory cells, and MSCs. The use of graft-specific exosomes for targeted drug therapy has the potential to reduce the unwanted side effects of immunosuppressive drugs. Overall, in this review, we have explored the critical role of exosomes in the recognition and cross-presentation of donor organ-specific antigens during allograft rejection. Additionally, we have discussed the potential of exosomes as a biomarker for monitoring graft function and damage, as well as their potential therapeutic applications in mitigating allograft rejection.

Domino Liver Transplantation for Unresectable Colon Cancer Liver Metastasis From a Donor With Heterozygous Familial Hyperlipidemia: A Case Report.

Liver transplantation (LT) is a potential curative treatment for unresectable colorectal cancer liver metastasis (CRLM). Familial hypercholesterolemia (FH) is an inherited condition characterized by elevated low-density lipoprotein cholesterol (LDL-C) levels. Liver transplantation is offered for selected cases, and an explanted liver can be used as a domino graft. We report the first report of domino LT for unresectable CRLM using a liver from a patient with heterozygous FH. The domino donor was a 30-year-old female with a history of heterozygous FH. She had failed medical therapies for FH, including plasmapheresis; therefore, she underwent living donor LT as a treatment for FH. The explanted liver was transplanted to the domino recipient. She has been doing well with normal LDL-C levels. The domino recipient was a 44-year-old female with a history of stage 4 sigmoid cancer with liver metastases, for which she underwent laparoscopic sigmoid colectomy and right hepatectomy. She developed unresectable lesions in the remnant left lobe, which were controlled well with chemotherapy; therefore, she underwent domino LT. She is doing well without recurrence at the 31-month follow-up. Domino LT from a donor with heterozygous FH is feasible for strictly selected patients with unresectable CRLM.

Calcineurin/nuclear factor of activated T cells and MAPK signaling induce TNF-{alpha} gene expression in pancreatic islet endocrine cells.

Cytokines contribute to pancreatic islet inflammation, leading to impaired glucose homeostasis and diabetic diseases. A plethora of data shows that proinflammatory cytokines are produced in pancreatic islets by infiltrating mononuclear immune cells. Here, we show that pancreatic islet α cells and ß cells express tumor necrosis factor-α (TNF-α) and other cytokines capable of promoting islet inflammation when exposed to interleukin-1ß (IL-1ß). Cytokine expression by ß cells was dependent on calcineurin (CN)/nuclear factor of activated T cells (NFAT) and MAPK signaling. NFAT associated with the TNF-α promoter in response to stimuli and synergistically activated promoter activity with ATF2 and c-Jun. In contrast, the ß-cell-specific transcriptional activator MafA could repress NFAT-mediated TNF-α gene expression whenever C/EBP-ß was bound to the promoter. NFAT differentially regulated the TNF-α gene depending upon the expression and MAPK-dependent activation of interacting basic leucine zipper partners in ß cells. Both p38 and JNK were required for induction of TNF-α mRNA and protein expression. Collectively, the data show that glucose and IL-1ß can activate signaling pathways, which control induction and repression of cytokines in pancreatic endocrine cells. Thus, by these mechanisms, pancreatic ß cells themselves may contribute to islet inflammation and their own immunological destruction in the pathogenesis of diabetes.

Implications of a positive crossmatch in liver transplantation: a 20-year review.

Whether a positive crossmatch result has any relevance to liver transplantation (LT) outcomes remains controversial. We assessed the impact of a positive crossmatch result on patient and graft survival and posttransplant complications. During a 20-year period, 2723 LT procedures with crossmatch results were identified: 2479 primary transplants and 244 retransplants. The rates of positive B cell and T cell crossmatches were 10.1% and 7.4%, respectively, for primary transplants and 14.6% and 6.4%, respectively, for retransplants (P = 0.049 for a B cell crossmatch). Across all primary transplants, females (P < 0.001) and patients with autoimmune hepatitis (P < 0.001) had greater frequencies of positive crossmatches. There was no effect from race or age. For both primary transplants and retransplants, patient survival and graft survival were not affected by the presence of a positive crossmatch. With respect to posttransplant complications, there were no differences in rejection episodes (hyperacute, acute, or chronic) or technical complications (biliary and vascular) between negative and positive crossmatch groups. However, there were significant differences in the pathological findings of preservation injury (PI) on liver biopsy samples taken at the time of transplantation and within the first week of transplantation (P = 0.003 for B cells and P = 0.03 for T cells). In summary, a positive crossmatch had no significant impact on patient survival or graft outcomes. However, there was a significantly higher incidence of PI in primary LT recipients with a positive crossmatch. This finding is important for a broader understanding of PI, which may include a significant immunological component.